JPH09175840A - Low-reflection glass substrate for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for a solar cell, having sufficiently suppressed reflection on the surface of the glass substrate to sufficiently increase the transmittance of sunlight and contributing to improve the conversion efficiency of a solar cell. SOLUTION: This low-reflection glass substrate for a solar cell is produced by forming a thin film 3 having a refractive index of n1 =1.7 to 1.9 and a thickness of d1 =70 to 85nm as the 1st thin film layer on a surface of a glass substrate 1 for solar cell and forming a thin film 4 having a refractive index of n=1.4 to 1.5 and a thickness of d2 =90 to 100nm as the 2nd thin film layer on the 1st thin film layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent glass substrate used in a solar cell, which has reduced reflection, and has a higher transmittance of visible light, an increased amount of incident sunlight, and a higher conversion efficiency. The present invention relates to a low reflection glass substrate for a solar cell, which can obtain an excellent solar cell.

[0002]

2. Description of the Related Art Conventionally, a low reflection glass substrate has been used. For example, Japanese Unexamined Patent Publication (Kokai) No. 2-60173 describes an Inp solar cell, which has an np-type layer on the sunlight incident side.
Type Inp solar cell, comprising a surface electrode and an insulating antireflection film formed on the n-type layer, and a conductive film formed on the antireflection film, wherein the surface electrode and the conductive film are It is disclosed that they are electrically connected.

Among them, as the antireflection film, for example, Si ₃ N ₄ , SiO ₂ , ZnS or the like is used in a single layer or in multiple layers, and as the conductive film, ITO (indium tin oxide), tin oxide, indium oxide is used. It is preferable that the thickness of the surface electrode be thicker than that of the antireflection film, that the antireflection film and the conductive film have minimum reflection loss of sunlight, and that the conductive film is as thin as possible. .

Further, as a condition of the antireflection film, nd = λ / 4 is used, where n is its refractive index, d is its thickness, and λ is the wavelength of light. The refractive index n of both the Si ₃ N ₄ film and the ITO film is approximately equal to 2.0, and the optimum wavelength λ of sunlight that maximizes the output is approximately 550 nm when calculated from the sunlight spectrum and the wavelength sensitivity characteristics of the Inp solar cell. Therefore, the optimum antireflection film thickness d is d = 1 / n.λ / 4 = 550 / 8nm = 6
It becomes 8.8 nm. It is described that the sum of the thickness of the ITO film and the film thickness of the Si ₃ N ₄ film is kept constant at 70 nm so that the reflection is minimum for sunlight having a wavelength of 550 to 600 nm.

In addition to this, for example, Japanese Patent Laid-Open No. 61-2372 describes that an ITO film alone is used as an antireflection film on the surface of a solar cell.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the Inp solar cell described in Japanese Patent No. 2-60173, it is difficult to say that the solar cell glass substrate has sufficiently reduced the reflection of sunlight and its transmittance has been sufficiently improved. Furthermore, the reflection loss and the absorption loss are improved. However, it was necessary to achieve high efficiency.

Si used in these solar cells and the like
In the case of a glass substrate on which a transparent conductive film of O ₂ or ITO is formed, a SiO ₂ thin film is generally used in order to prevent the alkaline component from being eluted from the glass and deteriorating the conductivity. (Passivation film) However, in this method, a SiO ₂ thin film having a low refractive index and a conductive film having a relatively high refractive index are formed in contact with each other, and the reflectance increases due to the interference of light and the incidence of sunlight. The amount of light will be reduced.

[0008]

The present invention has been made in view of the above-mentioned drawbacks of the prior art. For example, instead of a SiO ₂ film on one side, the refractive index is set to a value between the glass substrate and the transparent conductive film. A transparent glass substrate for a solar cell, which is formed by forming a thin film having the above and is configured to reduce reflection of sunlight, and the other surface (non-conductive film side) of the transparent glass substrate for a solar cell,
A thin film having the same refractive index and film thickness as described above, and a two-layer structure in which the thin film having a relatively low refractive index (n = 1.4 to about 1.5) and a specific film thickness is specified. By forming a laminated thin film layer that is appropriately combined with the system, the reflection of sunlight on the glass substrate surface (outer surface) is further reduced, the sunlight transmittance is increased, and the conversion efficiency is also improved to be excellent. The transparent low reflection glass substrate for solar cells is simply and efficiently provided.

That is, the present invention provides a thin film (1) layer having a refractive index of one surface of a glass substrate for solar cells from the glass surface side.
A thin film is formed in the range of n ₁ = 1.7 to 1.9 and d ₁ = 70 to 85 nm, and then the thin film (2) is formed on the thin film (1) layer.
The layer has a refractive index of n ₂ = 1.4 to 1.5 and a film thickness of d ₂
A low reflection glass substrate for a solar cell, which is formed by coating and laminating thin films having a thickness of 90 to 100 nm.

A thin film (3) layer having a refractive index of n ₃ = 1.45 to 2.00 and a film thickness of d ₃ = 60 to 120 nm is formed on the other surface of the low reflection glass substrate for solar cell. The low reflection glass substrate for a solar cell described above, which is formed.

Further, the above-mentioned solar cell characterized in that the thin film (1) layer and the thin film (3) layer have the same refractive index n ₁ and n ₃ and the film thickness d ₁ and d ₃ , respectively. Low reflection glass substrate. Furthermore, in the low reflection glass substrate for a solar cell, a transparent conductive thin film is formed on the thin film (3) layer, wherein the low reflection glass substrate for a solar cell described above.

Furthermore, the transparent conductive film has a refractive index
The low-reflection glass substrates for solar cells described above are characterized by having n ₀ = 1.8 to 2.2 and a film thickness of d ₀ = 500 to 700 nm.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Here, as a low reflection glass substrate for a solar cell, a thin film (1) layer having a refractive index of n ₁ = 1.7 to 1.9 on one side of the glass substrate for a solar cell is used. And, a thin film is formed in a film thickness range of d ₁ = 70 to 85 nm, and then a thin film (2) layer having a refractive index of n ₂ =
The reason that the thin film having a thickness of 1.4 to 1.5 and a film thickness of d ₂ = 90 to 100 nm is laminated is that the thin film (1) has an optical predetermined refractive index. For example Si
O ₂ film TiO ₂ (alone n = 2.20), or ZrO ₂ (alone n =
1.90), or a mixture of tantalum oxide and the like, and the refractive index is n ₁ = 1.7 to 1.9. When the refractive index is increased or decreased from the predetermined value, the reflectance at the wavelength at which the spectral reflectance exhibits a minimum value is 0%.
It becomes higher and the low reflection property deteriorates. In addition, since the refractive index of the thin film 2 is n ₂ = 1.4 to 1.5, the refractive index is
The SiO ₂ film, which is 1.45, is considerable. These thin films (1) and
Regarding the film thickness of (2), when the film thickness of both films is too thick, the wavelength at which the spectral reflectance has a minimum value shifts to the long wavelength side, and when it becomes thin, the wavelength shifts to the short wavelength side, and the reflectance is both It increases (that is, the transmittance decreases). For example, the wavelength at which the spectral reflectance has a minimum value is set to about 555 nm, which has the highest luminosity. Therefore, the thin film 1 has a film thickness of d ₁ = 70 to 85
In the range of nm, the thickness of the thin film 2 is d ₂ = 90 to 100 nm.

A thin film (3) layer having a refractive index of n ₃ = 1.45 to 2.00 and a film thickness of d ₃ = 60 to 120 nm is formed on the other surface of the low reflection glass substrate for solar cells. What was formed was a passivation film that prevents diffusion of sodium in the glass substrate for thin film (3).
The SiO ₂ film alone (n = 1.45 alone) or the SiO ₂ film mixed with TiO ₂ (n = 2.20 alone) or ZrO ₂ (n = 1.90 alone) is especially preferable. It is sufficient that the refractive index and the film thickness are such that a low reflection effect can be obtained together with the conductive film, for example, the Nesa film, and the refractive index is n ₃ = 1.45 to 2.00.
And the film thickness is d ₃ = 60 to 120 nm.

Further, the refractive indexes n ₁ and n ₃ and the film thicknesses d ₁ and d ₃ of the thin film (1) and the thin film (3) are not equal to each other within the above range. If thick,
It is preferable because it does not hinder the reduction of the reflection and simplifies the production.

Further, regarding the thin film (1), SiO ₂ ,
TiO _2, ZrO _2, Al ₂ O _3, B ₂ is preferably made of a mixture of two or more of O _3, a relatively high refractive index TiO ₂
(About 2.20), ZrO ₂ (about 1.90) and relatively low refractive index
By combining SiO ₂ (about 1.45), Al ₂ O ₃ (about 1.65), and B ₂ O ₃ (about 1.60) in various combinations, it is possible to freely control and obtain a composite with a refractive index of 1.7 to 1.9. This is because the film is easy to obtain and has excellent durability.

Furthermore, regarding the transparent conductive film,
Refractive index n ₀ = 1.8-2.2 and film thickness d ₀ = 500-700nm
Film such as NES film, ITO film, and the like, as long as they are within the ranges of the refractive index and the film thickness.

Further, as the glass substrate, a transparent float glass (Fl2) having a plate thickness of about 2 mm is most preferable, and if it is thin, the strength as a glass substrate becomes too low, and if it is too thick, the transmittance becomes low. The performance of the solar cell deteriorates. The plate thickness is preferably 1.0 to 3.0 mm, 1.5 to 2.5 m
About m is more desirable.

Needless to say, although it is disadvantageous in terms of cost, it is possible to use Optifine. It goes without saying that it can also be used as tempered glass, strength-up glass, bent glass, or the like. Further, it goes without saying that the glass substrate may be inorganic or organic.

As described above, the low reflection glass substrate for a solar cell of the present invention can reduce the sunlight reflectance as compared with the conventional glass substrate for a solar cell, and can reduce sunlight (visible light range) required for photovoltaic power generation. The amount of incident light is increased by, for example, about 6% at the maximum, which can sufficiently contribute to increase the light conversion efficiency in the solar cell.

The low reflection glass substrate for solar cells of the present invention can be used not only for amorphous solar cells but also for crystalline solar cells.

[0022]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to such an embodiment.

Example 1 First, Ti alkoxide and Si alkoxide were used in a molar ratio.
Prepare a diluted solution of ethanol in a mixed alkoxide of 55:45 so that the solute concentration is about 0.45 mol / l, and then mask the outer surface of a 2 mm thick clear glass with a masking tape. Approximately 3.8mm by immersing in the above prepared solution
After the dipping film is formed at the speed of 1 / sec, the masking tape
Peel off the film and heat at about 250 ° C for about 10 minutes to form a thin film (1).
A gel film of

Similarly, a masking tape was attached to the non-film surface of this glass, and the glass was dipped in a dilute solution of Si alkoxide in isopropyl alcohol prepared to have a solute concentration of about 0.25 mol / l, and the speed was about 3.0 mm / sec. After forming a film with
Peel off and heat at about 250 ° C for about 10 minutes to form a thin film (2).
A gel film of [As shown in FIG. ] Further, a masking tape is similarly applied to the film-laminated surface of this glass.
And dip it in a dilute solution of Si alkoxide in isopropyl alcohol adjusted to a solute concentration of about 0.25 mol / l.
After forming a film at a rate of about 2.9 mm / sec, the masking tape was peeled off, and the film was heated at about 250 ° C. for about 10 minutes to obtain a thin gel film (3). [As shown in FIG. Next, the coated glass substrate was cured at about 500 ° C. for about 30 minutes.

The obtained low reflection glass substrate for solar cell 1 shown in FIG. 2 is, as shown in Table 1, a thin film (1) having a refractive index n ₁ of about 1.79 and a film thickness on one surface of the substrate. d ₁ is about 77 nm, and as shown in FIG. 3, a low reflection glass having a laminated film having a refractive index n ₂ of about 1.45 and a film thickness d ₂ of about 95 nm as a thin film (2) thereon, On the other side of the glass, there is a thin film (3 as a single-layer passivation film with a refractive index n ₃ of about 1.45 and a film thickness d ₃ of about 100 nm. D ₀
A Nesa film (n ₀ = 2.00) which is a conductive film 7 having a thickness of about 600 nm is laminated [shown in FIG. 3]. ] And a low reflection surface (thin film (1), (2) side)
Therefore, the surface reflectance of visible light incident in the vertical direction is about 17.18% to about 14.23% of the conventional solar cell glass substrate (glass substrate with passivation film) without a low reflection film. It could be reduced by about 3%. Further, the visible light transmittance could be increased by about 3% from about 81.70% of the conventional glass substrate for a solar cell having no low reflection film to about 84.61%.

In addition to the dipping method, the film forming method according to the present invention may be, for example, a spin coat method, a cart coat method, a roll coat method or the like. Example 2 As in Example 1, a mixed alkoxide obtained by mixing a Ti alkoxide and a Si alkoxide in a molar ratio of 58:42 was mixed with isopropanol so that the solute concentration in terms of oxide was about 3.0 wt%. A diluted solution was prepared. This sol solution is uniformly supplied onto a roll coat which rotates at a speed of about 18 m / min, and a clear glass substrate having a thickness of 2 mm is placed on a conveyor belt under the roll coat at a speed of about 12 m / min. -Move in the opposite direction to the rotation of the glass substrate to apply the sol liquid on the glass substrate, and then dry this glass substrate at about 250 ° C for about 30 minutes,
A thin film (1) was obtained.

Next, Si alkoxide prepared with a dilute solution of isopropanol to a concentration of 1.8 wt% (as oxide) was added to
It is uniformly supplied onto a roll coat which rotates at a speed of about 6 m / min, and the clear glass substrate is moved under this at a speed of about 4 m / min in the opposite direction to the rotation of the roll, The thin film (2) was laminated on the thin film (1), and then this glass substrate was dried at about 250 ° C. for about 30 minutes to obtain a thin film (2). [As shown in FIG. Next, a mixed alkoxide in which a Ti alkoxide and a Si alkoxide are mixed at a molar ratio of 80:20,
An isopropanol-diluted solution was prepared so that the solute concentration in terms of oxide was about 3.0 wt%, and this sol solution was uniformly supplied onto a roll coat rotating at a speed of about 18 m / min. With the non-deposited surface of the two-layer laminated glass substrate facing up,
The sol liquid is applied on the glass substrate by moving the lower part of the rukot at a speed of about 8.5 m / min in the direction opposite to the rotation of the roll,
Then, this glass substrate was dried at about 250 ° C. for about 30 minutes to obtain a thin film (3). [As shown in FIG. Next, the coated glass substrate was cured at about 500 ° C. for about 30 minutes.

The obtained low reflection glass substrate for solar cell shown in FIG. 2 has a thin film on one surface of the substrate as shown in Table 1.
As (1), the refractive index n ₁ is about 1.79 and the film thickness d ₁ is about 77 nm, and as shown in FIG.
It is a low reflection glass having a laminated film with n ₂ of about 1.45 and a film thickness d ₂ of about 95 nm.The other surface of the glass is a thin film (3) with a refractive index n ₃ of about 2.00 and a film thickness d ₃ Is a single-layer passivation film of about 100 nm. On top of the thin film (3) a thickness d ₀
A Nesa film (n ₀ = 2.00) of about 600 nm is laminated [shown in FIG. 3]. ] And the surface reflectance of visible light incident vertically from the low reflection surface (thin films (1) and (2) side) is the same as that of a conventional glass substrate for solar cells (passive coating) without a low reflection film. -Glass substrate with ionization film) from about 17.35% to about 12.04% by about 5%. In addition, the visible light transmittance is about the same as that of a conventional glass substrate for solar cells without a low reflection film.
It was possible to increase by about 5% from 81.70% to about 86.80%.

The film forming method according to the present invention is a roll roll method.
Besides the spin coating method, for example, a spin coating method, a cart coating method, a dipping method or the like is also possible. Example 3 As in Example 1, a mixed alkoxide obtained by mixing a Ti alkoxide and a Si alkoxide in a molar ratio of 55:45 was mixed with a diluted solution of ethanol having a solute concentration of about 0.45 mol / l. After preparing, then dipping a clear glass substrate with a thickness of 2 mm into the above-prepared solution to form a dipping film at about 3.8 mm / sec, and then heating at about 250 ° C. for about 10 minutes, the thin film (1) and the thin film (3 ) Was obtained. The thin film (2) was applied onto the thin film (1) in the same manner as in Example 2, and then the glass substrate was dried at about 250 ° C. for about 30 minutes to obtain a thin film (2). [As shown in FIG. Next, the coated glass substrate was heat-treated at about 500 ° C. for about 30 minutes.

The obtained low reflection glass substrate for a solar cell shown in FIG. 2 is, as shown in Table 1, thin films (1) and (3) having a refractive index n ₁ and n ₃ of about 1.79 and a film thickness d. ₁ and d ₃ are about 77 nm,
A low reflection glass having a laminated film having a refractive index n ₂ of about 1.45 and a film thickness d ₂ of about 95 nm on the thin film (1) as shown in FIG. ), A Nesa film (n ₀ = 2.00) with a thickness d _{0 of} about 600 nm is laminated on the low reflection surface (thin film (1)
, (2) side), the surface reflectance of visible light incident in the vertical direction is about 17.35% of that of a conventional solar cell glass substrate (glass substrate with a passivation film) without a low reflection film. It was possible to reduce it from about 11.27% to about 6%. In addition, the visible light transmittance could be increased by about 6% from about 81.70% of the conventional glass substrate for solar cells without a low reflection film to about 87.59%. Comparative Example 1 The outer surface of a clear glass substrate having a thickness of 2 mm was masked with a masking tape, immersed in a dilute solution of Si alkoxide in isopropyl alcohol prepared to have a solute concentration of about 0.25 mol / l, and a speed of about 2.9 mm / sec. After forming a film with
Peel off the tape and heat at about 250 ° C for about 10 minutes to form a thin film (3).
I got [As shown in FIG. Next, the coated glass substrate was heat-treated at about 500 ° C. for about 30 minutes.

The obtained glass substrate for solar cells shown in FIG. 4 has a refractive index n ₃ of about 1.45 and a film thickness d _{3 as} shown in Table 1.
Is a glass substrate with a single-layer passivation silica film of about 100 nm. If a Nesa film having a thickness of about 600 nm similar to that of the embodiment is laminated on this passivation silica film, its surface reflectance with respect to visible light incident in the vertical direction is about
The high visible light transmittance is 17.18% and the low visible light transmittance is about 81.70%.

Comparative Example 2 As in Example 1, a mixed alkoxide obtained by mixing a Ti alkoxide and a Si alkoxide in a molar ratio of 80:20 had a solute concentration in terms of oxide of about 3.0 wt%. Prepare a dilute solution of isopropanol so that
It is uniformly supplied onto a roll coat rotating at a speed of 18 m / min, and below this a float glass substrate having a thickness of 2 mm is approximately 8.5 m / min.
The roll is moved in the direction opposite to the rotation of the roll at a speed of a minute to apply the sol liquid onto the glass substrate, and then the glass substrate is moved to about
A thin film (3) was obtained by drying at 250 ° C for about 30 minutes. [As shown in FIG. Next, this was heat-treated at about 500 ° C. for about 30 minutes.

The obtained glass substrate for a solar cell shown in FIG. 4 has a refractive index n ₃ of about 2.00 and a film thickness d _{3 as} shown in Table 1.
Is a glass substrate with a single-layer passivation silica film of about 100 nm. A thickness of about 60 is applied on this passivation film.
When the same NESA film as in the example of 0 nm is laminated, the surface reflectance for visible light incident in the vertical direction is about 15.17.
%, And the visible light transmittance is about 83.71%, which is higher than that of the glass substrate for a solar cell of Comparative Example 1, but does not satisfy the intended performance of the present invention. It was

[0034]

[Table 1]

[0035]

As described in detail above, according to the present invention,
By appropriately combining thin films having the specified refractive index and film thickness on one side or both sides of a glass substrate, in particular, by providing a laminated film of two layers on at least the air side glass surface, it is possible to obtain more sunlight than conventional glass substrates for solar cells. The reflectance can be reduced,
The incident light amount of sunlight (visible light range) required for solar power generation is
For example, it is possible to provide a useful low-reflection glass substrate for a solar cell, which can be increased by about 6% at the maximum and can sufficiently contribute to increase the light conversion efficiency in the solar cell.

[Brief description of the drawings]

FIG. 1 is a partially enlarged side sectional view showing an example of a low reflection glass substrate for a solar cell of the present invention.

FIG. 2 is a side sectional view showing a partially enlarged low reflection glass substrate for a solar cell of the present invention in each example.

FIG. 3 is a side cross-sectional view showing a partially enlarged state of a conductive film (nesa film) laminated on the low reflection glass substrate for a solar cell of the present invention shown in FIG.

FIG. 4 is a side cross-sectional view showing a partially enlarged glass substrate for a solar cell in Comparative Example 1.

[Explanation of Codes] 1 low reflection glass substrate for solar cell 2 glass substrate 3 thin film (1) 4 thin film (2) 5 thin film (3) 7 conductive film 8 glass substrate for solar cell 9 visible light transmittance T 10 visible light reflection Ratio R ₁ 11 Visible light reflectance R ₂ 12 a-Si side 13 Air side

Claims (5)

[Claims] 1. A thin film (1) layer having a refractive index of n ₁ = 1.7 to 1.9 and a film thickness of d ₁ = 70 to 85 nm as a thin film (1) layer on one surface of a glass substrate for a solar cell from the glass surface side. On the thin film (1) layer, and the refractive index n ₂
= 1.4 to 1.5 and a film thickness of d ₂ = 90 to 100 nm, which is formed by coating and laminating thin films for solar cells. 2. A thin film (3) layer having a refractive index n ₃ = 1.45 to 2.00 and a film thickness d ₃ = 60 to 120 nm on the other surface of the low reflection glass substrate for solar cells. The low reflection glass substrate for a solar cell according to claim 1, which is formed. 3. The thin film (1) layer and the thin film (3) layer have the same refractive index n ₁ and n ₃ and the same film thickness d ₁ and d ₃ , respectively. Low reflection glass substrate for solar cells. 4. The low reflection glass substrate for solar cells according to claim 2, wherein in the low reflection glass substrate for solar cells, a transparent conductive thin film is formed on the thin film (3) layer. . 5. The transparent conductive film has a refractive index of n ₀ = 1.8
The low reflection glass substrate for a solar cell according to claim 4, wherein the thickness is 2.2 and the film thickness is d ₀ = 500 to 700 nm.